Selectively hydrogenated block copolymer-polystyrene blends

ABSTRACT

MOLDING COMPOSITION HAVINE HIGH IMPACT STRENGTH AND IMPROVED OXIDATIVE STABILITY ARE PREPARED BY PHYSICALLY BLENDING A POLYMER OF AT LEAST ONE MONOVINYL AROMATIC COMPOUND WITH A BLOCK COMPOLYMER PREPARED BY SELCTIVELY HYDROGENATING TO SUBSTANTIALLY COMPLETE SATURATION THE DIENE PORTION OF A BLOCK COPOLYMER HAVING AT LEAST TWO POLYMER BLOCKS OF A MONOVINYL ARENE SEPARATED BY AT LEAST ONE POLYMER BLOCK PREDOMINATELY OF A CONJUGATED DIENE. THIS INVENTION RELATES TO HIGH IMPACT THERMOPLASTIC COMPOSITIONS OF POLYMERS OF MONOVINYL AROMATIC HYDROCARBONS AND TO A PROESS FOR PREPARING THEM MORE PARTICULARLY, THE INVENTION PROVIDES A PROCESS FOR PREPARING HIGH IMPACT THERMOPKASTIC MOLDING COMPOSITIONS, ESPECIALLY POLYSTYRENE, HAVING IMPROVED OXIDATIVE STABILITY.

United States Patent 3,810,957 SELECTIVELY HY DROGENATED BLOCKCOPOLYMER-POLYSTYRENE BLENDS Hans E. Lunk, Menlo Park, Calif., assignorto Shell Oil Company, Houston, Tex.

No Drawing. Continuation-impart of application Ser. No.

62,698, Aug. 10, 1970, which is a continuation of application Ser. No.463,892, June 14, 1965, both now abandoned. This application Feb. 7,1972, Ser. No. 224,316

Int. Cl. C08f 41/12 US. Cl. 260-876 B 10 Claims ABSTRACT OF THEDISCLOSURE Molding compositions having high impact strength and improvedoxidative stability are prepared by physically blending a polymer of atleast one monovinyl aromatic compound with a block copolymer prepared byselectively hydrogenating to substantially complete saturation the dieneportion of a block copolymer having at least two polymer blocks of amonovinyl arene separated by at least one polymer block predominately ofa conjugated diene.

This invention relates to high impact thermoplastic compositions ofpolymers of monovinyl aromatic hydrocarbons and to a process forpreparing them. More particularly, the invention provides a process forpreparing high impact thermoplastic molding compositions, especiallypolystyrene, having improved oxidative stability.

This application is a continuation-in-part of Ser. No. 62,698, filedAug. 10, 1970 now abandoned, which, in turn, is a continuation of Ser.No. 463,892, filed June 14, 1965, now abandoned.

BACKGROUND OF THE INVENTION Conventionally high impact poly(monovinylaromatic) molding compositions such as polystyrene contain polymericstyrene and a rubber polymer. It is known that good compositions may beobtained by physical blending, e.g., polystyrene with rubber or bymixing the rubber polymer with monomeric styrene and graft polymerizingthe mixture. Many types of rubber materials have been employed includingnatural rubber, styrene-butadiene copolymer .(GRS rubber) andpolybutadiene. These polystyrene compositions while having acceptablehigh impact strength, do not have good weather resistance, that is theydo not have good oxidation stability, and they deteriorate rapidly withexposure to sunlight with the concomitant reduction of the impactstrength to an undesirably low value.

STATEMENT OF THE INVENTION A principal object of the present inventionis to provide high impact thermoplastic poly(monovinyl aromatic) moldingcompositions, having greatly improved oxidative stability. Anotherobject is to provide a process for preparing high impact polystyrenemolding compositions having improved weathering resistance, that is,resistance against oxidation and particularly against ultra-violetdeterioration. Other objects will be apparent to one skilled in the artfrom the following disclosure and discussion.

Specifically, the invention provides a high impact resinous compositionof polymerized monovinyl aromatic hydrocarbons, particularly styrene,which comprises a blend of said polymerized monovinyl aromatichydrocarbon with a block polymer prepared by selectively hydrogenatingthe diene portion of a block copolymer having at least two polymerblocks of a monovinyl arene separated by at least one polymer block of aconjugated diene. The invention further provides a process for preparinghigh impact thermoplastic molding compositions having 3,810,957 PatentedMay 14, 1974 improved oxidation stability which comprises physicallyblending from 60 to parts by weight of a resinous polymer of a monovinylaromatic hydrocarbon, preferably polystyrene, with from about 10 toabout 40 parts by weight of a block copolymer prepared by selectivelyhydrogenating the diene portion of a block polymer having at least twopolymer blocks of a monovinyl arene separated by at least one polymerblock of a conjugated diene.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Suitable polymers of monovinylaromatic hydrocarbons are prepared by polymerizing at least onemonoalkenyl aromatic hydrocarbon of the benzene series and include thepolymers of styrene and ring-substituted styrene Wherein the aromaticnucleus is substituted with one or more alkyl groups preferablycontaining from about 1 to 4 carbon atoms such as methyl or ethyl orwith a halogen group such as a ehloro group. Examples of such monomersare vinyl toluene, vinyl xylene, vinyl ethyl benzene and vinylchlorobenzene. Suitable monomers also include the chain-substitutedstyrenes such as alpha-methylstyrene. Preferably, these polymers have anintrinsic viscosity of from about 0.5 to about 15, especially in therange from about 0.6 to about 1.0 dl./g., as determined using a 0.25 g./ml. solution in toluene at 30 C.

The block copolymers suitable for hydrogenation and subsequent use inthe present invention have at least two polymer blocks A wherein each Arepresents a polymer block of a monovinyl arene, separated by at leastone polymer block B wherein each lB represents a polymer block ofhomopolymer or copolymer of a conjugated diene wherein the dienepredominates. In the following discussion and description, when anyblock copolymer is described in which two blocks B are immediatelyadjacent to each other, e.g., in a polymer such as the adjacent blocks Bare considered as a single polymer block for purposes of molecularweight. Accordingly, within the above generic descriptiomthe blockcopoly mers suitable for hydrogenation may have a general configurationselected from A-B-A, A'B-A) and AB-{B-A) wherein A and B are defined ashereinabove.

The end blocks, A, which may comprise from about 25 to about 50% andpreferably from about 32 to about 45% of the total block copolymer, havemolecular weights from about 5,000 to about 75,000, and more preferablyfrom about 8,000 to about 60,000; and any nonadjacent center blocks, B,have an average molecular weight from about 30,000 to about 300,000, andmore preferably from about 50,000 to about 300,000. In conformance withpreceding statements, any blocks B adjacent to each other have a totalaverage molecular weight from about 30,000 to about 300,000 and morepreferably from about 50,000 to about 300,000.

Preferably, the block copolymers, prior to selective hydrogenation arethose in which each polymer block B is a homopolymer or copolymer of atleast one conjugated diene hydrocarbon, preferably alltadiene, having 4to 10 carbon atoms per molecule such as butadiene, isoprene, piperyleneand ethyl butadiene or diene copolymer containing up to 35% by weight onblock B of a monovinyl arene such as styrene or alpha methyl styrenedistributed therein in a non-block, i.e., random or taperedconfiguration. Most preferred are conjugated dienes having 4 or 5 carbonatoms per molecule. Preferably, the block copolymers are those in whichthe end blocks, A, prior to hydrogenation (and afterwards) comprise atleast one monovinyl arene such as styrene, the ring alkylated styrenes,

such as t-butylstyrene, ring halogenated styrenes such as thechlorostyrenes, and alpha-methylstyrene.

A typical, but by no means exhaustive, list of suitable block polymersincludes the following:

Polystyrene-polybutadiene-polystyrenePolystyrene-polyisoprcue-polystyrene Polystyrene-polybutadiene(polybutadienepolystyrene) Polystyrene- (polyisoprene-polystyrene)Polystyrene-poly(ethyl-butadiene)-polystyrene Polystyrene-p oly (randombutadiene-styrene) -polystyrenePoly(alpha-methylstyrene)-polybutadiene-poly(alphamethylstyrene) Polyalpha-methylstyrene) -polyisoprene-poly alphamethylstyrene)Poly(styrene-alpha-methylstyrene)-poly(butadieneisoprene)(styrenealpha-methylstyrene) Poly (vinylxylene) -polybutadiene-poly(vinylxylene) The processes for the preparation of such block copolymersdo not form a part of the present invention. Briefly, however, the blockcopolymers are formed either by sequential polymerization in thepresence of a catalyst capable of forming a living polymer such as butyllithium under conditions well known in the block copolymer art or by thecoupling of preformed polymer blocks.

These poly(monovinyl aromatic hydrocarbon)-poly (conjugateddiene)-poly(monovinyl aromatic hydrocarbon) block copolymers are thenselectively hydrogenated, i.e., the conjugated diene portion ishydrogenated to substantially complete saturation and the vinyl aromaticportion is left substantially unhydrogenated, e.g., less than 5%,preferably less than 2% hydrogenated.

The processes for hydrogenation of the block copolymers form no part ofthe present invention. Briefly, however, suitable catalysts comprise areduced metal form of a member selected from the group consisting ofcobalt, nickel, manganese, tungsten and molybdenum, as well as mixturesthereof, wherein said reduced metal form is obtained by reacting acompound of the above metals with a metal-compound reducing agent.Suitable organo metallic reducing agents include aluminum hydride andhydrocarbyl aluminum compounds of from 3 to 35 carbon atoms, especiallytrihydrocarbyl aluminum compounds of from 3 to 35 carbon atoms permolecule. The freshly reduced compositions may be prepared and used ashydrogenation catalysts in situ or may be separated prior to use.Although heating is not required for catalyst formation, temperatures offrom about 0 C. and 250 C. may be employed.

The ratios of organometallic reducing agents to reduce able metalcompounds may range from about 0.1 to 30.1.

The catalyst may be prepared either in slurry form or mounted on asuitable support.

In general, any source of molecular metal may be employed. Metal saltsmay be used as well as organometallic compounds and coordinationcomplexes. Salts of organic acids may be used with salts of alkanoicacids with from 1 to 12 carbon atoms in the alkanoate moiety beingpreferred. Especially preferred are compounds such as dicobaltoctacarbonyl.

The polymers to be hydrogenated are preferably dissolved in a suitablesolvent or in a mixture of solvents. Unsaturated solvents such asbenzene or toluene may be employed, but saturated solvents such ascyclohexane, iso-octane, neopentane, and 2,4-dimethyl hexane arepreferred.

It is generally possible to selectively hydrogenate to substantialcompletion, i.e., at least 90% saturation, the above copolymers attemperatures below about 150 C. with the above-described catalysts.Under suitable conditions at least 99% of the diene units of thecopolymer are normally saturated and less than 1% and generally lessthan 0.5% of the arene portions of the copolymers are converted.Hydrogenation is more selective as the .4 temperature is reduced, buthydrogenation time is correspondingly extended. Consequently,temperatures between about 25 and 150 C. are preferred for the selectivehydrogenation of the diene portion of the block polymer.

As noted above, the time required for hydrogenation will depend upon thecatalyst concentration, extent of hydrogenation desired and thetemperature employed. In general, however, the diene portion of thecopolymer is substantially completely hydrogenated in from about 0.05 toabout 8 hours. As will be understood, any arene in each block B is notconverted by hydrogenation.

The above discussion of the selective hydrogenation is a briefdescription because it alone is not novel with applicant. Thehydrogenation process is described in greater detail in application Ser.No. 333,671, filed Dec. 26, 1963, by Myron G. Quam and Milton M. Wald, acontinuation-in-part application of which is now US. 3,595,942.

In general, the block copolymers particularly useful for the presentinvention include the poly(monovinyl aromatichydrocarbon)-poly(conjugated diene having from 4 to 10 carbonatoms)-poly(monovinyl aromatic hydrocarbon) which has been subsequentlyselectively hydrogenated to substantial completion, i.e., the conjugateddiene portion is at least saturated and preferably at least saturatedand most preferably at least 99% saturated. As noted hereinbefore, thepoly(monovinyl aromatic hydrocarbon) portion is not significantlyhydrogenated. The poly(monovinyl aromatic hydrocarbon) blocks, A,preferably have a molecular weight in the range from about 8,000 toabout 60,000 and the poly (conjugated diene) block(s) B have a molecularweight from about 30,000 to about 300,000, with the proviso that anyblocks B which are adjacent to each other are treated as a singlepolymer block segment having a total average molecular weight from about30,000 to about 300,000.

An especially preferred hydrogenated block copolymer is the blockpolymer of polystyrene-polyisoprene-polystyrene which has beenhydrogenated to a polystyrene-poly (ethylene/propylene)-polystyreneblock polymer. Preferably, the polyisoprene block to be hydrogenatedcontains substantial, i.e., above about 70% cis 1,4 content.

Another preferred hydrogenated block copolymer is prepared byhydrogenating a polystyrene-polybutadienepolystyrene block polymerwherein the polybutadiene is a rubbery polybutadiene having a suitable1,2-polybutadiene up to 1,4-polybutadiene ratio, i.e., from about 30:70to about 70:30, and especially from about 35:65 to about 55:45. Themicrostructure of the polybutadiene may be determined by conventionalinfra-red analysis according to procedure of Silas et al., AnalyticalChemistry, vol. 31, pp. 529-532 (1959).

Thus, the polymer chain of the B block contains a plurality of pendantlower alkyl substituent, e.g., methyl, ethyl and the like, distributedsubstantially throughout, which substituent may be found on up to about70% of the carbon atoms in the polymer chain.

The hydrogenated block polymers may be physically blended with thepoly(monovinyl aromatic hydrocarbons) by any of the well-known methodssuch as by milling, extruding and mixing (Banbury mixer). In general,the physical blending is performed at a temperature from about to about270 C., preferably from about to 250 C. Higher and lower temperaturesmay also be employed.

Although the ratio of hydrogenated block polymer to poly(monovinylaromatic hydrocarbon) can vary quite widely depending upon the desiredend use of the molding compositions, in general, from about 10 to 40parts by weight of the hydrogenated block copolymer is physicallyblended with from 60 to 90 parts by weight of the poly(monovinylaromatic hydrocarbon), with from about 15 to 30 parts by weight of thehydrogenated block copolymer to about 70 to 85 parts by weight ofpoly(monovinyl aromatic hydrocarbon) being preferred. Generally,

selectively hydrogenated block copolymers having higher total molecularweight B blocks, e.g., above about 90,000, are more effective forenhancing impact strength at lower concentrations in the final blend.

Inert ingredients such as conventional filler materials for thepolystyrene, e.g., silicas, carbon black, talc, titanium oxides and thelike; antioxidants such as, e.g., 2,6- di-tert-butyl-4-n1ethyl phenoland/or trisnonylphenyl phosphite; and light stabilizers such as the2-alkyl-2,3,4- benzotriazoles may be added to the molding composition.They may be added at any convenient time during the preparation of themolding composition of this invention.

It is also generally desirable to add a lubricant in order to improvemoldability of the composition, and any of the known lubricants may beused in this invention. Examples of lubricants include ester lubricantssuch as butyl stearate, mineral oil, parafiin wax and combinations ofthese lubricants.

Advantages of the present invention are illustrated by the followingexamples. The reactants, their proportions and other specificingredients are presented as being typical and various modifications canbe made in view of the foregoing disclosure and discussion withoutdeparting from the spirit or scope of the specification or of theclaims. Unless otherwise stated, parts and percentages are by weight.Impact data are in ft. lbs/in. of notch at 23 C.

EXAMPLE I This example illustrates the high impact strength exhibited bythe novel polystyrene molding compositions of the present invention.

A polystyrene-poly (ethylene/propylene) polystyrene block polymer havinga molecular weight. of about 30,- 000100,00030,000 was prepared byselectively hydrogenating the diene portion to substantial completion,i.e., (99%+), a polystyrene-polyisoprene-polystyrene block polymer as a7% cyclohexane cement at 800 p.s.i. and 160 C. using a catalystcomprising cobalt acetate reduced with aluminum triethyl with analuminum:cobalt ratio 2:1.

Various amounts of this block copolymer were physically blended withpolystyrene in a 6-inch roll mill at 185 C. for 10 minutes.

Styrene molding compositions were also prepared by physically blendingan ethylene-propylene rubber and a styrene-butadiene rubber'(SBR) withpolystyrene. The physical properties of these molding compositions aretabulated in Table I.

It is seen that polystyrene poly(ethylene/propylene)- polystyrene blockpolymers impart excellent impact strength as well as very good hardnessand yield strength and are superior to conventional polystyrene moldingcompositions employing conventional rubbers.

TABLE I Izod impact Hardness Yield Elon- Polyvinyl aromatic strength,Rockstrength, gation, molding composition It.-lbs./in. well M p.s.i.percent 85 parts polystyrene plus parts of polystyrcnepoly(ethylene/propylene)-polystyrene block polymer (SEPS) 0. 86 10 3, 640 5 80 partspolystyrene plus parts SEPS 1. 24. 2 3, 380 8 75 parts polystyrene plusparts SEPS 3. 36 8 3, 050 8 70 parts polystyrene plus parts SEPS 4. 2514 2, 450 40 80 parts polystyrene plus 20 parts ethylenepropylene rubber1 0. 29 -11 70 parts polystyrene plus 30 parts ethylenepropylone rubber0.21 42 75 parts polystyrene plus 25 parts of SBR a 1. 82 20 2, 850 40./g. 8-1006 containing 23% styrene and 77% butadiene.

6 EXAMPLE II TABLE II Impact izod Initial strength izod after Retentionimpact 1,000 of impact strength, hours strength. Polystyrene moldingcomposition ft.-lbs./in. exposure percent Polystyrene-SB R blend 1. 820. 65 36 Polystyrene-SEPS blend 8. 36 3. 26 97 EXAMPLE III This exampleillustrates that selective hydrogenation of the conjugated dieneportions of the block copolymer results in good impact properties whichare not obtained with fully hydrogenated block copolymer.

A series of blends were prepared from a commercial homopolystyrene andvarious amounts of a block c0- polymer ofpolystyrene-polybutadiene-polystyrene having a molecular weight of about25,000-100,00025,000 wherein the polybutadiene portion, which containedabout 40% by weight of 1,2 units had been hydrogenated selectively toabout 99% saturation; and less than about 1% of the polystyrene endblocks had been hydrogenated (SEB S) wherein EB represents an ethylenebutene copolymer. The hydrogenated block polymer, therefore, containedabout 33% of the original unsaturation. The blends which were preparedon an electrically heated 3 inch mill exhibited the physical propertiestabulated in Table III.

This procedure was repeated to prepare blends of 16 and 26% blockcopolymer except that for these blends the block copolymer was the sameblock copolymer, however, fully hydrogenated to remove essentially allof the unsaturation from the polystyrene end blocks, thereby chemicallyconverting them to polymer blocks of vinyl cyclohexane (C--EB --C). Thecomposition and physical properties of these blends is also shown inTable III.

TABLE III Hardness Izod impact Rock- Rock Polyvinyl aromatic moldingstrength, well well composition it.-lbs./in. R M

A.-.-. Polystyrene base polymer 0.2 120 72 B Blends with selectivelyhydro- 0.3 113 35 genated block copolymer, parts polystyrene, 10 partspolystyrene-poly (ethylene/ butylcne)-polystyrene (sEB4q-S 84 partspolystyrene, 16 parts 1.3 104 2.6

EB4Q S 80 parts polystyrene, 20 parts 2.1 99 -7.5

B -S). 74 partsBpolystyrene, 26 parts 3.6 88 -l3.6

41r- C Blends with fully hydrogenated 0.4 100 1.8

block copolymers, 84 parts polystyrene, 16 parts poly-(vinylcyelohexane)poly(ethylenelbutylene)poly(vinylcyclohexane)(C-EB4C). 74 parts polystyrene, 26 parts 0.4 77 -15.8

EB C).

To lllustrate the suitability of the composltions with selectivelyhydrogenated block copolymer for in ection 7 molding an additional blendof 20 parts by weight of the above selectively hydrogenated blockcopolymer and 80 parts by weight of polystyrene was prepared in aBanbury mixer, subsequently extruded through a strand die and choppedinto nibs. The blend which was then injection molded had the followingtensile properties:

Tensile modulus, p.s.i 390,000 Yield strength, p.s.i 4,400 Breakingstrength, p.s.i 3,700 Elongation at break, percent 18+ EXAMPLE IV Tofurther illustrate the invention a series of blends were prepared from acommercial homopolystyrene and various amounts of a block copolymer ofpolystyrenepolybutadiene-polystyrene having a molecular weight of25,000-88,00023,000 wherein the polybutadiene portion contained about40% 1,2 units had been selectively hydrogenated to about 99% saturationand less than about 1% of the polystyrene end blocks had beenhydrogenated. The block copolymer, therefore, contained about 35% f theoriginal unsaturation. The blends were prepared by mixing in a BrabenderPlasticorder for ten minutes at about 200 C. under nitrogen. Propertiesof the blends may be seen in Table IV. The above procedure was repeatedexcept that the same block copolymer had been hydrogenated to removeapproximately 75% of the unsaturation of polystyrene end blocks inaddition to full hydrogenation of the center block. This additionallyhydrogenated block copolymer therefore, contained about 9% of theoriginal unsaturation. The composition and properties of these blendsalso appear in Table IV.

TABLE IV Hardness Izod impact Rock- Rock Polyvinyl aromatic moldingStrength, well well composition ft.-lhs./in. R M

A- Blends with selectively hydro- 1. 1 101 3. 2

genated block copolymer 84 parts polystyrene 16 parts polystyrene-polyethylene] butylelgieypolystyrene 40 80 parts polystyrene, 20 parts 1. 494 -9. 4

(S-EB S). 74 parts polystyrene, 26 parts 1. 9 77 -14 (S-EB S). B Blendswith additionally hy- 0. 4 94 5.6

drogenated block copolymer, 84 parts polystyrene, 16 partspoly(vinylcyclohexane/styrene)-poly(ethylene/butylene)-poly(vinylcyclohexane/ styrene) (C SEBCS) 80 parts polystyrene, 20 parts 0. 4 90 9. 1

(OSEB4uCS). 74 parts polystyrene, 26 parts 0. 4 65 -18 (CS-EBm-CS).

What is claimed is:

1. A process for preparing a high impact thermoplastic moldingcomposition having improved oxidation stability which comprisesphysically blending from 70 to 85 parts by weight of a resinous polymerconsisting of at least one monovinyl aromatic hydrocarbon selected fromstyrene, a-methylstyrene and ring substituted styrenes wherein thearomatic nucleus bears at least one substituent selected from alkylgroups of 1 to 4 carbon atoms and halogens, with from about 30 to aboutparts by weight of a selectively hydrogenated block copolymer having atleast two polymer blocks A separated by at least one polymer block Bwherein prior to hydrogenation, each A is a polymer block of a monovinylarene having a molecular weight in the range from about 5,000 to about75,000

said blocks A comprising from 25 to 50% by weight of the total blockcopolymer and B is a polymer block having a molecular weight from about30,000 to about 300,000 formed from a conjugated diene selected fromhomopolymers of at least one conjugated diene having 4 to 10 carbonatoms per molecule and random and tapered copolymers of said conjugateddiene with up to 35% by weight on block B of a monovinyl arene, with theproviso that any adjacent blocks B are treated as a single polymer blocksegment having a total segment molecular weight from about 30,000 toabout 300,000; and after hydrogenation the diene portion of said blockcopolymer is at least 95% saturated, and less than about 2% of the areneblocks are converted.

2. A high impact thermoplastic molding composition having improvedoxidation stability comprising a physical blend of (a) 70 to parts byWeight of a resinous polymer consisting of at least one monovinylaromatic hydrocarbon selected from styrene, a-methylstyrene and ringsubstituted styrene wherein the aromatic nucleus bears at least onesubstituent selected from alkyl groups of 1 to 4 carbon atoms andhalogens; and (b) 30 to 15 parts by weight of a selectively hydrogenatedblock copolymer having at least two polymer blocks A separated by atleast one polymer block B wherein, prior to hydrogenation, A is apolymer block of a monovinyl arene and having a molecular weight in therange from about 5,000 to about 75,000; said blocks A comprising from 25to 50% by weight of the total block copolymer and B is a polymer blockhaving a molecular weight from about 30,000 to about 300,000 formed froma conjugated diene selected from homopolymers of at least one conjugateddiene having from 4 to 10 carbon atoms per molecule and random andtapered copolymers of said conjugated diene with up to 35% by weight ofa monovinyl arene and with the proviso that adjacent blocks B aretreated as a single polymer block segment having a total segmentmolecular weight from about 30,000 to about 300,000; and afterhydrogenation the diene portion of said block copolymer is at leastsaturated and less than about 2% of the arene blocks are converted.

3. A composition as in claim 2 wherein the resinous polymer is selectedfrom polymers of styrene, alpha methyl styrene and mixtures thereof.

4. A composition as in claim 2 wherein B is a polymer block of aconjugated diene having 4 or 5 carbon atoms.

5. A composition as in claim 2 wherein the resinous polymer ispolystyrene and the block copolymer prior to hydrogenation has theconfiguration polystyrene-polybutadiene-polystyrene wherein thepolybutadiene has a ratio of 1,2 polybutadiene to 1,4 polybutadiene fromabout 30:70 to about 70:30.

6. A composition as in claim 2 wherein the block copolymer prior tohydrogenation is polystyrene-polyisoprene-polystyrene and wherein thepolyisoprene portion is selectively hydrogenated to at least 99%saturation.

7. A composition as in claim 2 wherein in the block copolymer blocks Aare polymer blocks of monomers selected from styrene, alpha methylstyrene and mixtures thereof and having a molecular weight in the rangefrom about 8,000 to about 60,000 and block B is a polymer block having amolecular weight from about 50,000 to about 300,000 formed from aconjugated diene having from 4 or 5 carbon atoms per molecule, with theproviso that any adjacent blocks B are treated as a single polymer blocksegment having a total segment molecular weight from about 50,000 toabout 300,000 and after hydrogenation the diene portion of said blockcopolymer is at least 95 saturated and less than about 1% of the areneportions are converted.

8. A composition as in claim 2v wherein the block copolymer blocks A arealpha methyl styrene blocks.

hydrogenation has the general configuration selected from 5 A-B-A,A{-BA) and A-B{-B--A) wherein A represents a polymer block of amonovinyl arene said end blocks A together comprising from 32 and 45% ofthe total block copolymer and, B represents a polymer block of ahomopolymer of an alkadiene having 4 or 5 10 carbon atoms.

1 0 References Cited UNITED STATES PATENTS 3,231,635 1/ 1966 Holden etal. 260-876 3,299,174 1/1967 Kuhre et a1. 260876 MURRAY TILLMAN, PrimaryExaminer C. J. SECCURO, Assistant Examiner US. Cl. X.R.

260-285 B, 41.5 R, 41.5 A, 45.7 P, 45.95, 878 B, 880 B

